(1) Technical Field
This disclosure relates generally to the field of white LED drivers and relates more specifically to white LED drivers preventing ringing in Discontinuous Conduction Mode.
(2) Background
White light emitting diodes (WLED) are used most often in notebooks and desktop screens, and in virtually all mobile LCD screens. A WLED is typically a blue LED with broad-spectrum yellow phosphor to give the impression of white light. WLEDs are often used for backlighting LCD displays. For such an application WLED drivers have to generate constant current required for a constant luminance.
Inductive boost converters are often used as WLED drivers, generating high bias voltages from a single low-voltage supply, such as a battery. Ringing of the current in the coil of the inductive boost converter caused by parasitic charging and discharging of the switching node LX results in EMI radiation and input/output noise by parasitic coupling.
A common solution is to introduce a switch across the coil to virtually dump the oscillations when ringing occurs, while it remains open when the power switch is on. This represents a certain level of complication for the integrated technology in use for such WLED boost converter.
Therefore it is a challenge for engineers designing high voltage WLED drivers to find a simple solution for the ringing problem and to keep the system efficient.